Garrido-Ramos M A, de la Herrán R, Ruiz Rejón M, Ruiz Rejón C
Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Spain.
Genome. 1999 Jun;42(3):442-6.
In an ongoing effort to trace the evolution of the sex chromosomes of Silene latifolia, we have searched for the existence of repetitive sequences specific to these chromosomes in the genome of this species by direct isolation from low-melting agarose gels of satellite DNA bands generated by digestion with restriction enzymes. Five monomeric units belonging to a highly repetitive family isolated from Silene latifolia, the SacI family, have been cloned and characterized. The consensus sequence of the repetitive units is 313 bp in length (however, high variability exists for monomer length variants) and 52.9% in AT. Repeating units are tandemly arranged at the subtelomeric regions of the chromosomes in this species. The sequence does not possess direct or inverted sequences of significant length, but short direct repeats are scattered throughout the monomer sequence. Several short sequence motives resemble degenerate monomers of the telomere repeat sequence of plants (TTTAGGG), confirming a tight association between this subtelomeric satellite DNA and the telomere repeats. Our approach in this work confirms that SacI satellite DNA sequences are among the most abundant in the genome of S. latifolia and, on the other hand, that satellite DNA sequences specific of sex chromosomes are absent in this species. This agrees with a sex determination system less cytogenetically diverged from a bisexual state than the system present in other plant species, such as R. acetosa, or at least a lesser degree of differentiation between the sex chromosomes of S. latifolia and the autosomes.
为了持续追踪宽叶蝇子草性染色体的进化过程，我们通过从限制性内切酶消化产生的卫星DNA条带的低熔点琼脂糖凝胶中直接分离，在该物种的基因组中寻找这些染色体特有的重复序列。从宽叶蝇子草中分离出的属于一个高度重复家族的五个单体单元，即SacI家族，已被克隆并进行了表征。重复单元的共有序列长度为313 bp（然而，单体长度变体存在高度变异性），AT含量为52.9%。重复单元在该物种染色体的亚端粒区域串联排列。该序列不具有显著长度的正向或反向序列，但短正向重复序列散布在整个单体序列中。几个短序列基序类似于植物端粒重复序列（TTTAGGG）的简并单体，证实了这种亚端粒卫星DNA与端粒重复序列之间的紧密关联。我们在这项工作中的方法证实，SacI卫星DNA序列是宽叶蝇子草基因组中最丰富的序列之一，另一方面，该物种不存在性染色体特有的卫星DNA序列。这与一种性别决定系统相符，该系统在细胞遗传学上与两性状态的差异小于其他植物物种（如酸模）中存在的系统，或者至少宽叶蝇子草的性染色体与常染色体之间的分化程度较低。
